help with css colours

Yes that is how we spell colour in this part of the world, but that is not the issue.

OK, here is the problem: I have three columns of information on a page, positioned within divs using css (code to follow). One contains more content than the other. The problem is that the background colour only fills to the bottom of the content, not to the bottom of the page. How can I make it go to the bottom, without going back to tables?